Table 5

Effect of SHS exposure on exercise capacity through mediators

Mediators	Mediation analysis of effect of SHS exposure to
	Watts_Peak			Work_Total			VO_2Peak
	N	% mediated	P value	N	% mediated	P value	N	% mediated	P value
Cardiovascular outputs
Peaks
O₂-Pulse_Peak	241	40.8 (4.4 to 76.2)	0.038	235	73.6 (–170.7 to 319.8)	0.112		N/A *
HR_Peak	241	0.03 (–33.5 to 21.5)	0.998	235	8.0 (–106.2 to 112.8)	0.750	241	1.6 (–109.5 to 55.6)	0.962
SBP_Peak	223	2.5 (–17.4 to 23.0)	0.718	221	4.8 (–74.5 to 79.9)	0.736	223	3.2 (–53.4 to 42.3)	0.726
DBP_Peak	223	0.2 (–11.9 to 12.9)	0.892	221	0.5 (–28.8 to 47.5)	0.884	223	0.3 (–20.5 to 32.0)	0.894
Slopes
O₂-Pulse_Slope	234	11.7 (–7.4 to 37.9)	0.214	234	14.1 (–81.6 to 101.9)	0.278		N/A *
HR_Slope	234	17.6 (–0.6 to 49.7)	0.058	234	18.9 (–80.6 to 138.7)	0.160	234	13.2 (–4.6 to 75.4)	0.114
SBP_Slope	224	1.7 (–30.5 to 24.0)	0.848	222	0.7 (–53.9 to 38.4)	0.868	224	1.0 (–53.8 to 30.8)	0.882
DBP_Slope	224	1.9 (–31.1 to 25.0)	0.840	222	0.7 (–83.2 to 44.9)	0.934	224	2.1 (–75.4 to 39.1)	0.852
Pulmonary outputs
RR_Peak	231	7.3 (–19.9 to 34.0)	0.474	229	26.3 (–167.8 to 217.8)	0.294	231	18.1 (–82.2 to 90.2)	0.462
VE_Peak	241	30.0 (–13.4 to 61.7)	0.116	235	70.4 (–166.1 to 277.7)	0.116	241	58.9 (–47.9 to 156.9)	0.106
VT_Peak	235	11.5 (–17.4 to 38.8)	0.300	233	14.8 (–61.5 to 124.4)	0.398	235	13.7 (–35.4 to 74.9)	0.316
RV/TLC	234	7.3 (–7.0 to 42.2)	0.284	229	10.5 (–59.2 to 134.9)	0.310	234	8.1 (–14.3 to 99.9)	0.318
FRC/TLC	219	4.3 (–4.8 to 31.1)	0.276	218	5.2 (–30.1 to 73.1)	0.366	219	6.6 (–9.7 to 83.5)	0.256

To see if the association of SHS exposure (independent variable) with exercise capacity (dependent variable) was mediated through the cardiovascular or pulmonary outputs, mediation analyses were performed with adjustment for age, sex, height and body mass index and inclusion of one mediator at a time. Statistically significant values are shown in bold.
*The associations of VO_2Peak with O2-Pulse_Peak and O2-Pulse_Slope were not computed due to existence of “mathematical coupling” between VO₂ and O₂-Pulse, which depends on VO₂ for its calculation (O₂-Pulse=VO₂/HR).
DBP, diastolic blood pressure; FRC, functional residual capacity; HR, heart rate; O₂-Pulse_Peak, oxygen uptake per heartbeat at peak exercise; RR_Peak, peak respiratory rate; RV, residual volume; SBP, systolic blood pressure; SHS, secondhand smoke; TLC, total lung capacity; VE_Peak, peak minute ventilation value; VO_2Peak, peak oxygen uptake; VT_Peak, peak tidal volume.